Air conditioning system



W. L. MSGRATH A IR CONDITIONING SYSTEM March 2s, 1944.

Filed sept. 1s, 1941 Y 4 z IIIIII... u llll IIJ, J z u n u m m A Mu. l 7 e. .1, s, M a 1 l n 3 3/5 .2 .u 1 m Q I 1 w u AJ m H i a ,f .2.. U 1 Il fflllLl. n l a n v Ein en 3 8 4 I l IJ m u 1 F uv Pv 7- Z A, mv a s v 1 .m .u .IIIIIIIL a l. l l l l .IIL 2 2 2 d raceteam?. ze, 1944 UNITED STATES PATENT oFFlcE' am coNnxz'rziiiiG SYSTEM v William `L. McGrath, Philadelphia, Pa., assignor to Minneapolsloneywell Regulator Company, Minneapolis, Minn., a corporation of Delaware i i Applicatitn september 1s, 1941, serial No. 411,348

Ffclaims.

Thisvinvention relates in general to heat exchange'control and more particularly to automatic controlsystems` for maintaining proper temperature conditions within a conditioned space. t f

In the heating art it has become common to heat rooms'in buildings by means of devices .known as unit ^ventilators. Theseunit ventilalocted at the space being heated, each containing aheating coil and a fan for forcing a circulation of the air over the coil. The heating ef- A feet of. these .coils is usually controlled either by means of valves which control the flow of heatingl medium through the coils or by means of face` ad'by-pass dempers `which control the flow of air through the coils, these valves or dampers be- -ing graduatingly controlled by means of thermoltially open the damper and will cause too much heat to be supplied to the space thus causing the space temperature to again rise which again causes complete closure of the face damper. Thus `to`rs consist of relatively small units which are y stats responsive to the temperature of the spaces trolling thermostat and provides 'arange of. mcdulation of the valve or damper for Jany heating load While at' the same time rendering the sys- 'tem capable of adjusting itself to carry the heating load regardless of whether it is large or small.

`In addition, this supplemental control, by lower ing the temperature of` the heating medium in mild weatherdiverses the heat dissipation from the piping and thus avoids any overheating from this cause.

While the invention is of particular utility and is described in particular as applied to control of heating, it is equally adapted for control of cooling. Also, while the invention is described as applied to a system for controlling building temperature it is not limited to this branch in the art of heat exchange but is of broad application.'

Other objects of the invention will appear from the followingv description and' the appended claims.

Fora full disclosure Yof this invention'reierence` is m'ade to the following description and to the accompanying drawing, the single figure of which instead of providing proper modulating control,

the thermostat causes the damper to constantly cycle between completely closed position and 'a partially open. position. This causes warm and cold air to be alternately supplied to the space`I which causes discomfort of the occupants. This "cycling also wastes heat ldue to the intermittentv overheating action and'also reduces the life of the thermostatic controls due to the continual operation.'

It is an object of ltliisdxiventioxi to provide a v system of the type mentioned which 'overcomes the dimculty describedprovidlng proper control of the unit or mits duringvmlld weather as well f as during cold weather. fIn accordance with this invention, the 'heating medium 'to the unit or unitsis controlled .in'response to the change'in temperature ofthe medium passed through the coils, in addition to the control of the-units in accordance with space temperature. This supplem'ental control reduces the effect for a given movement-of` the valve or; damper by the conillustrates diagrammatically the invention as applied to a heating system. y

- Referring to the drawing, reference character l indicates a hot water boiler having a firing means such as an oil burner -2 which is controlled by a thermostat 3 responsive to the temperature ofthe heated water. This boiler is `connected to a supply mainl which conveys Aheated water to the various zones and is also provided with return mains 5 and 6. The supply main 4 is connected by ai pipe 'l to one inlet of a three-way valve 8 and the discharge of this valve 8'is 'connected toa branch main 9 which includes a circulator I0. 'Ihis branch main 9` is connected to the heatingA coils il of unit ventilator devices I2. AThe unit ventilators I2 may be of usual conl struction and may each consist of a casing I3 having openings I4 -and l5 for admission of fresh and recirculated air, the proportions being controlled by a damperv 16. The unit ventilators I2 also may each be provided with a partition such as I1 which forms a by-pass passage for the air around the heating coil Il. Each unit ventilator also is provided with a fan such as 'I8 for forcing circulationr of air therethrough.. The controlof airfthroughy the heating coil Il and the by-pass passage of each unit ventilator'may be controlled by means o'f a face damper I9' and a by-pass1 damper 20 which are actuated in unison butin inverse order by means of .a motorZl.

This motor maybe ofthe type shown and de scribed i the Taylor Patent"2',028,1l0 andl may temperature oi' the return water. 35 is connected by a capillary tube 38 to a control 2 be controlled by means ofa thermostat 22 which responds to the temperature of the space heated by the corresponding unit ventilator. With the arrangement described, upon decrease in temperature the motor 2l will position dampers I9 and so as to increase the ilowof air through coil Il thereby increasing' the heating eil'ect oi' the unit ventilatori Conversely, upon increase in temperature'the thermostat 22 will opcrate to decreasethe ilow of air through coil II thereby decreasing the amount of .heating performed.

" In systems as heretofore used the coil I I of each asses?? are supplied tothe unitventilatorsf yIf the slider 32 engages the lower endgof resistance 3 3, the

motor 30 will -position valve 8 so as to supply all recirculated water to the branch main 9, and if the slider 32 engages the upper end of resistance 33 the motor 30 .will position valve 8 at its opposite extremity wherein all hot water is supplied to the branch. supply main 9.

Operation VIn operation, assuming that the heating load v upon the system is at a maximum, the various unit ventilator remains at constant temperature.

This causes improper operation during mild, weather,` for a very slight opening'of the face damper I9 will provide appreciable heating. thus causing overheating of the space whenever the I thermostat opens the face damper even slightly.

This causes lthe face damper i! to be continually shifted by the motor 2! from completely closed position to slightly open position and back to closed position which results in alternately sup plying warm and cold air tothe space which is undesirable. Y

The three-way valve 8 is lprovided for the p' pose of avoiding the undesirable action Just described. This three-way valve includes a second inlet which is connected by pipe 25 with the branch return main 26 which leads from the outlet of the coils in unit ventilators I2 tothe return main 6. A It will be apparent that by positioning the three-way valve l the proportions of thermostats 2 2 will position the damp'ers of the unit ventilators for causing amaximumilowof air across the heating coils.- This will cause the water in flowing through the heating coilsfto be cooled considerably which will resultin the slider f 32 engaging the upper end of resistance 33 for supplying all heated water to the heating ele'- ments.

across the various heating elements I I. This reduction in air flow across the coils will reduce 1 the amount of-heat removed from the. Water heated water from the main 4 and the recircuwith a `resistance 33 to form fa control poten-A tiometer for the proportioning motor 30. This lever is actuated by opposed bellows 34 and 3B. 'I'he bellows 3l is connected by a capillary tube 3I 'to a control bulb 31 mounted upon the branch return main 28. This causes the pressure within bellows 3.4 to vary in accordance with the The bellows bulb 39 which responds to the temperature of in passing through the coils thus causing thedifvferential between the' Supply. and returnwater to decrease. This will'cause movement .of the slider 32 downwardly across resistance 33 for causing the proportioning motor 30 to position valve 8 for admitting recirculated water from the pipe 25 to the branch supply main 9. This position of the valve 8 will thus lower the temperatureof the water being supplied to the unit ventilators. It will be apparent that as the output of the unit ventilators iscontinually decreasedin response to decrease in load, the differential in temperature 4between the supply and returnv way terwill continue to decrease which will cause the valve 8 to increase more and more the ',pro-

the-water iiowing through the supply branch main 8. As the bellows 3l and 35 act in opposition it will be apparent fthat the slider 32 is positioned upon resistance 33 in accordance with the diiferential in temperature between the water being supplied to the heating coils of the ventilators andthe water leaving said coils. The controller 3|- may also be provided'with a biasinglprins 4l for determining the differential. fin temperature maintained'between the supply and return branch mains.

. The' ends of resistence 33 and the slider 32 oi controller 3| are connected to the. proportionins motor IIL motor 30 to position the three-.way'valve 8 proportionately to the position of'slid'er 32" upon resistance 33. Thusif s1ider`.32 engages thecenter of resistance 33 the proportioning motor will cause the valve I to assume mid position where- This causes the proportioning.

' a differential thermostat 3Ia.

inl equal amounts of hot andrecirculated water 75.

portion of recirculated water. Thus duringm'ild weathenwhen only very little heat is withdrawn from the circulated water by the heating coils II, thethree-way valve 8 will be positioned for supplying only a small amount ot hot-water" to the heating coils which will cause 'these heating coils to operate at relatively low temperature. Due to these heating coils operating at the'. low temperature, the thermostats 22 may opennthe4 face dempers I9 appreciably without overheating the space and thus true-modulating control is obtained down to a minimum heat output.

In utilizing this invention the building may be divided into zones having different `heating requirements and the temperature oi' the water supplied to each zone may be varied by separate three-way valves which are controlled by the diilerential in temperature between the supply and return water. Thus if desired, an additional zone may be utilized consisting ofunit ventilators I2a which are controlled by means of thermostats 22a, these' ventilators being connected to branch supply and return mains 9a and '26s.' This additional zone may be controlled by a separate three-way valve 8a which is positioned by a proportioning motor 30a under the control of From the foregoing description it. will be apparent that the present invention provides for i automatically reducingHthe temperature' of the heating coils of the 'unit ventilators in response tofthe heating -load upon the system for thereby l permitting the controlling dampers to be opened appreciably even in mild weather. without causing overheating of the space and thus provides for true modulation oi the heatingthroughout As the-load upon the-system decreases, -the thermostats 22 will reduce the flow of air the entire control range. While the invention is particularly applicable to heating systems, it may also be used in cooling systems and in other types of heat exchange systems generally. While I have shown and described a preferred form of the invention, it will be apparent that many changes may be made Without departing from the scope of the invention. I therefore desire to beflimited only by the Scope of the append-ed claims.

I cla-im as my invention:

1. In a system of the class described, in combination, a heat exchange device through which heat exchange fluid is passed for controlling the temperature of a medium, a first controller for graduatingly controlling the flow of said medium across said heat exchange device, a second controller for controlling the temperature of the heat exchange fluid circulated through said heat exchange device, and means responsive to the differential in temperature ,of the heat exchange fluid before and after it ilovvs through said *heat exchange device for controlling said 'second controller.

2. In a system of the class described, in combination, a heat exchange device through which heat exchange uid is passed, means for passing air over said device and to a space to be conditioned, temperature responsive means for controlling the transfer of heat from said heat exchange device to said air, means for varying the temperature of the heat exchange iiuid supplied to said heat exchange device, and means -responsive to the diierential in temperature of the heat exchange fluid before and after it ows through said heat exchange device for controlling said last mentioned means in a manner to reduce its heat exchange capacity upon a decrease in said temperature diierential.

3. In a temperature controlling system :for a space, in combination, a conditioning chamber through which air supplied to the space is passed, a heat exchange device in said conditioning chamber, a controller for varying the ow of air through said conditioning chamber, means responsive to space temperature for controlling said controller to vary the ow of air through said heat exchange device in a manner tending to maintain the space temperature constant, means ior'supplying heat exchange uid to2 said heat exchange device, means including valve means for introducing heat exchange -uid which has passed through said heat exchange device into the heat exchange fluid being passed to said heat exchange device for changing the temperature of the uid delivered to said heat exchange device, and means responsive to the differential in temperature of the heat exchange fluid before and after it passes through said heat exchange device for controlling said valve means.

4.. In a system of the class described, in cornbination, a plurality of heat exchange devices, common supply and return conduits for said heat exchange devices for circulating heat exchange 5. In a system of the class described, in combination, a plurality of heat exchange devices associated with a plurality of diierent locations to be conditioned, common supply and return conduits for circulating heat exchange uid throughv said heat exchange devices, means for passing air over each of said heat exchange devices, controllers associated with each of said heat exchange devices for controlling the flow of air through said devices in a manner tending to maintain proper temperature conditions atthe various locations, valve means associated with said supply and return conduits for introducing diierent proportions of heat exchange iuid from said return conduit into said supply conduit to thereby change the temperature of the fluid supplied to said heat exchange devices, and means responsive to the difference in temperature of the heat exchange fluid in the supply and return conduits for controlling said valve means.

6. In a heating system for a space, in combination, a radiating element, means for controlling the quantity of air passing over said radiating element, thermostatic means responsive to the temperature of the space in control of said lastnamed means, means for supplying a heated fluid to said radiating element including a connection for returning to said element iiuid which has already passed therethrough, valve means arranged to vary the proportions of heated and recirculated uid supplied to said radiating ele- `ment, and means responsive to the difference in temperature between the heated iiuid andthe fluid leaving said radiating element for operating said valve means in a manner to supply less heated iiuid and more recirculated fluid upon a decrease in such temperature differential.

7. In a system of the class described, in combination, a heat exchange device through which heat exchange iiuid is passed for controlling the temperature of a medium, a rst controller for graduatingly controlling the tlow of said medium across said heat exchange device, a second controller for controlling the temperature of the heat exchange iiuid circulated through said heat exchange device, and means responsive to the differential in temperature of the heat exchange iluid before and after it ilows through said heat exchange device for controlling said second controller, the rate of circulation of said heat exchange uid remaining substantially constant throughout the heating period.

v WILLIAM L. MCGRATH. 

